Doing More With Analog Input (Data Acquisition Toolbox)

Data Acquisition Toolbox

Recording and Retrieving Event Information

For some of the events listed above, certain information is automatically stored in the EventLog property. EventLog is a structure that contains two fields: Type and Data. The Type field contains the event type. The event types that are logged for analog input objects are start, stop, trigger, runtime error, input over-range, and data missed events. Data-available events and timer events are not logged to EventLog.

The Data field contains the event-specific subfields shown below.

**Table 4-8: EventLog Subfields**
Events	Data Subfield	Description
`All events`	TimeStamp	The absolute time the event occurred.
`All events`	SampleStamp	The number of samples acquired when the event occurred. The sample count begins when the `start` function is issued. A value of -1 indicates the engine was not running when the event ocurred.
`Trigger`	Channel	Which channels caused the trigger to be issued (used only for software triggers).
`Trigger`	Trigger	The trigger number
`Input over-range`	Channel	The channels that experienced an input over-range condition
`Input over-range`	Direction	Indicates if the over-range condition switched from "On" to "Off" or from "Off" to "On".
`Data missed`	Channel	The channel(s) from which data was missed.

The example below illustrates how you can retrieve event information.

Example: Retrieving Event Information

Suppose you want to examine the events logged for the voice activation example on page 4-32. You can do this by accessing the EventLog property.

events = AIVoice.EventLog

By examining the contents of the Type field, you can list the events that occurred during this acquisition.

{events.Type}
ans = 
    'Start'    'Trigger'    'Stop'

Note:
Unless a runtime error occurs, all acquisitions must have a start, trigger, and stop event.

The Data field of the trigger event recorded the absolute time the trigger occurred, the number of samples acquired since the start event occurred, the index of the trigger channel, and the trigger number.

trigdata = events(2).Data
trigdata = 
      TimeStamp: 7.3001e+005
    SampleStamp: 19342
        Channel: 1
        Trigger: 1

[ Previous | Help Desk | Next ]